The present invention relates to edible water-in-oil microemulsions that are transparent or translucent in appearance.
A microemulsion is considered to be a thermodynamically or kinetically stable liquid dispersion of an oil phase and a water phase, in combination with a surfactant. The dispersed phase typically comprises small particles or droplets, with a size range of 5 nm-200 nm, giving rise to a microemulsion that is transparent or translucent in appearance. This is in contrast to regular (macro-) emulsions that are turbid. The droplets or particles of the microemulsion may be spherical, although other structures are possible. The microemulsion is formed readily and sometimes spontaneously, generally without high-energy input. In many cases a cosurfactant or cosolvent is used in addition to the surfactant, the oil phase and the water phase.
Water-in-oil microemulsions have the advantage, due to their stability, of a long shelf life. Moreover, as the water phase droplets are usually extremely small, the microemulsions have good microbiological stability. This is in contrast to regular emulsions where the presence of water droplets can present a severe microbiological problem. Microemulsions also enable the water phase to be dispersed homogeneously throughout the oil phase without the necessity of using a structurant, since no phase separation will occur.
It is desirable to be able to prepare edible water-in-oil microemulsions for use as, or in, food products, which microemulsions comprise oils obtainable from readily available natural sources (eg. vegetable oils). In addition or in the alternative, it is desirable to prepare edible water-in-oil microemulsions that contain relatively large amounts of water. The inclusion of water reduces the calorific value of the microemulsion and enables the inclusion of water-soluble components, such as flavours, vitamins, salts, sugars, colorants and fragrances, to the benefit of the food product being or containing the microemulsion.
However, edible microemulsions are not easy to prepare, particularly those containing relatively large amounts of water and/or containing oils obtainable from natural sources.
In the prior art, Kahlweit et al (Langmuir, 11, 11, 4185, 1995) discloses an edible microemulsion using n-alkane-1,2-diols as cosurfactant and lecithin as surfactant. The oil phase is an oleic acid ethyl ester or iso-propylmyristate. It is therefore not based on readily available oils from natural sources like vegetable oil.
U.S. Pat. No. 5,045,337 relates to a water-in-oil microemulsion comprising a polyglycerol ester. The microemulsion contains up to 5% water or other polar solvent. The surfactants disclosed are polyglycerols in general, with restrictions to the amounts of mono-, di-, tri-, and tetraglycerols. The total amount of surfactants is limited to 10%. A stated object of the invention is to make a microemulsion which is free of a cosurfactant such as an alcohol or acid.
GB2297759 describes microemulsions that may be used in foodstuffs. It refers to the microemulsions of U.S. Pat. No. 5,045,337 by stating that it is important to minimise the amount of surfactant used to stabilise a given amount of water. The surfactant used in GB2297759 is a polyglycerol ester of an unsaturated fatty acid having from 12 to 24 carbon atoms. The polyglycerol component of the polyglycerol ester has at least 70% by weight of triglycerols or tetraglycerols. In GB2297759 the weight ratio of surfactant to water in the microemulsion is stated to be as low as 5:1 and the amount of water in the microemulsion is preferably less than 2% by weight. Thus, the microemulsion disclosed is not very efficient at solubilising water.
EP0657104 relates to edible water-in-oil microemulsions containing up to 33% water. The surfactants disclosed are diglyceride esters with a strong polar hydrophilic head group in combination with a monoglyceride. Examples of these surfactants are phospholipids, citrates, tartrates and lactilates. The oil phase comprises triglycerides. Various oils including sunflower oil and medium chain triglycerides are exemplified. Generally, the amounts of surfactants are rather high. A reasonably high water:surfactant ratio is obtained only with the use of medium chain triglycerides.
WO99/62357 discloses flavour-releasing compositions comprising water-in-oil microemulsion droplets and/or hydrated reverse micelles containing latent flavours. The compositions may be used as flavour delivery systems in foodstuffs, where the active flavour may be produced by the action of an enzyme. In the preferred embodiments the mole ratio of water to surfactant is preferably less than 10, and preferably less than 5. These systems are therefore better described as hydrated reverse micelles rather than microemulsions. In the single example, a microemulsion containing 3.0% water is prepared.
WO99/59422 discloses a water-in-oil emulsified fat composition containing specific diglycerides in a high concentration and suitable for use as a margarine or fat spread. The oil phase comprises 40-95 wt % diglycerides and 5-60 wt % triglycerides. The diglycerides are defined in terms of the levels and types of their saturated and unsaturated fatty acid groups. The diglycerides generally have a melting point of 20 C., preferably 30 C., in order to make a spreadable margarine or spread. A wide range of emulsifying agents is disclosed including lecithins. Nothing is mentioned about the formation of microemulsions or transparent emulsions.
The present invention seeks to provide an edible water-in-oil microemulsion that is transparent or translucent in appearance and that contains relatively large amounts of water.
The present invention also seeks to provide an edible water-in-oil microemulsion that is transparent or translucent in appearance and that contains oil obtainable from natural sources.
According to the present invention there is provided an edible water-in-oil microemulsion that is transparent or translucent in appearance, the microemulsion comprising oil, a surfactant, a cosurfactant or cosolvent and a water phase comprising water and optional water-soluble components; wherein the oil comprises from 25 to 97 wt % diglycerides relative to the total weight of glycerides.